remove the Subst trait, always use EarlyBinder

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -16,7 +16,7 @@ use rustc_middle::mir::{
     FakeReadCause, LocalDecl, LocalInfo, LocalKind, Location, Operand, Place, PlaceRef,
     ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind, VarBindingForm,
 };
-use rustc_middle::ty::{self, subst::Subst, suggest_constraining_type_params, PredicateKind, Ty};
+use rustc_middle::ty::{self, suggest_constraining_type_params, PredicateKind, Ty};
 use rustc_mir_dataflow::move_paths::{InitKind, MoveOutIndex, MovePathIndex};
 use rustc_span::def_id::LocalDefId;
 use rustc_span::hygiene::DesugaringKind;

compiler/rustc_borrowck/src/universal_regions.rs

@@ -22,8 +22,8 @@ use rustc_hir::{BodyOwnerKind, HirId};
 use rustc_index::vec::{Idx, IndexVec};
 use rustc_infer::infer::{InferCtxt, NllRegionVariableOrigin};
 use rustc_middle::ty::fold::TypeFoldable;
-use rustc_middle::ty::subst::{InternalSubsts, Subst, SubstsRef};
 use rustc_middle::ty::{self, InlineConstSubsts, InlineConstSubstsParts, RegionVid, Ty, TyCtxt};
+use rustc_middle::ty::{InternalSubsts, SubstsRef};
 use std::iter;
 
 use crate::nll::ToRegionVid;

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -13,7 +13,7 @@ use rustc_middle::mir::pretty::display_allocation;
 use rustc_middle::traits::Reveal;
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::print::with_no_trimmed_paths;
-use rustc_middle::ty::{self, subst::Subst, TyCtxt};
+use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::source_map::Span;
 use rustc_target::abi::{self, Abi};
 use std::borrow::Cow;

compiler/rustc_const_eval/src/interpret/intrinsics/caller_location.rs

@@ -4,7 +4,6 @@ use rustc_ast::Mutability;
 use rustc_hir::lang_items::LangItem;
 use rustc_middle::mir::TerminatorKind;
 use rustc_middle::ty::layout::LayoutOf;
-use rustc_middle::ty::subst::Subst;
 use rustc_span::{Span, Symbol};
 
 use crate::interpret::{

compiler/rustc_const_eval/src/transform/validate.rs

@@ -13,7 +13,6 @@ use rustc_middle::mir::{
     TerminatorKind, UnOp, START_BLOCK,
 };
 use rustc_middle::ty::fold::BottomUpFolder;
-use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, InstanceDef, ParamEnv, Ty, TyCtxt, TypeFoldable, TypeVisitable};
 use rustc_mir_dataflow::impls::MaybeStorageLive;
 use rustc_mir_dataflow::storage::always_storage_live_locals;

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -69,8 +69,8 @@ use rustc_middle::dep_graph::DepContext;
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::relate::{self, RelateResult, TypeRelation};
 use rustc_middle::ty::{
-    self, error::TypeError, Binder, List, Region, Subst, Ty, TyCtxt, TypeFoldable,
-    TypeSuperVisitable, TypeVisitable,
+    self, error::TypeError, Binder, List, Region, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
+    TypeVisitable,
 };
 use rustc_span::{sym, symbol::kw, BytePos, DesugaringKind, Pos, Span};
 use rustc_target::spec::abi;

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -15,8 +15,8 @@ use rustc_middle::hir::nested_filter;
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
 use rustc_middle::ty::print::{FmtPrinter, PrettyPrinter, Print, Printer};
-use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst, SubstsRef};
 use rustc_middle::ty::{self, DefIdTree, InferConst};
+use rustc_middle::ty::{GenericArg, GenericArgKind, SubstsRef};
 use rustc_middle::ty::{IsSuggestable, Ty, TyCtxt, TypeckResults};
 use rustc_session::SessionDiagnostic;
 use rustc_span::symbol::{kw, Ident};

compiler/rustc_infer/src/infer/opaque_types.rs

@@ -8,7 +8,7 @@ use rustc_data_structures::vec_map::VecMap;
 use rustc_hir as hir;
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::fold::BottomUpFolder;
-use rustc_middle::ty::subst::{GenericArgKind, Subst};
+use rustc_middle::ty::GenericArgKind;
 use rustc_middle::ty::{
     self, OpaqueHiddenType, OpaqueTypeKey, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
     TypeVisitable, TypeVisitor,

compiler/rustc_infer/src/infer/outlives/verify.rs

@@ -5,7 +5,7 @@ use crate::infer::{GenericKind, VerifyBound};
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::sso::SsoHashSet;
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::subst::{GenericArg, Subst};
+use rustc_middle::ty::GenericArg;
 use rustc_middle::ty::{self, EarlyBinder, OutlivesPredicate, Ty, TyCtxt};
 
 use smallvec::smallvec;

compiler/rustc_middle/src/mir/mod.rs

@@ -9,10 +9,10 @@ use crate::mir::visit::MirVisitable;
 use crate::ty::codec::{TyDecoder, TyEncoder};
 use crate::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeSuperFoldable};
 use crate::ty::print::{FmtPrinter, Printer};
-use crate::ty::subst::{GenericArg, InternalSubsts, Subst, SubstsRef};
 use crate::ty::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor};
 use crate::ty::{self, List, Ty, TyCtxt};
 use crate::ty::{AdtDef, InstanceDef, ScalarInt, UserTypeAnnotationIndex};
+use crate::ty::{GenericArg, InternalSubsts, SubstsRef};
 
 use rustc_data_structures::captures::Captures;
 use rustc_errors::ErrorGuaranteed;

compiler/rustc_middle/src/mir/tcx.rs

@@ -4,7 +4,6 @@
  */
 
 use crate::mir::*;
-use crate::ty::subst::Subst;
 use crate::ty::{self, Ty, TyCtxt};
 use rustc_hir as hir;
 use rustc_target::abi::VariantIdx;

compiler/rustc_middle/src/ty/abstract_const.rs

@@ -1,7 +1,7 @@
 //! A subset of a mir body used for const evaluatability checking.
 use crate::mir;
 use crate::ty::visit::TypeVisitable;
-use crate::ty::{self, subst::Subst, DelaySpanBugEmitted, EarlyBinder, SubstsRef, Ty, TyCtxt};
+use crate::ty::{self, DelaySpanBugEmitted, EarlyBinder, SubstsRef, Ty, TyCtxt};
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def_id::DefId;
 use std::cmp;

compiler/rustc_middle/src/ty/context.rs

@@ -15,7 +15,6 @@ use crate::mir::{
 use crate::thir::Thir;
 use crate::traits;
 use crate::ty::query::{self, TyCtxtAt};
-use crate::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, Subst, SubstsRef, UserSubsts};
 use crate::ty::{
     self, AdtDef, AdtDefData, AdtKind, Binder, BindingMode, BoundVar, CanonicalPolyFnSig,
     ClosureSizeProfileData, Const, ConstS, ConstVid, DefIdTree, ExistentialPredicate, FloatTy,
@@ -24,6 +23,7 @@ use crate::ty::{
     RegionKind, ReprOptions, TraitObjectVisitor, Ty, TyKind, TyS, TyVar, TyVid, TypeAndMut, UintTy,
     Visibility,
 };
+use crate::ty::{GenericArg, GenericArgKind, InternalSubsts, SubstsRef, UserSubsts};
 use rustc_ast as ast;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};

compiler/rustc_middle/src/ty/generics.rs

@@ -1,6 +1,5 @@
 use crate::ty;
-use crate::ty::subst::{Subst, SubstsRef};
-use crate::ty::EarlyBinder;
+use crate::ty::{EarlyBinder, SubstsRef};
 use rustc_ast as ast;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::def_id::DefId;

compiler/rustc_middle/src/ty/instance.rs

@@ -1,9 +1,7 @@
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::ty::print::{FmtPrinter, Printer};
-use crate::ty::subst::{InternalSubsts, Subst};
-use crate::ty::{
-    self, EarlyBinder, SubstsRef, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable, TypeVisitable,
-};
+use crate::ty::{self, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable, TypeVisitable};
+use crate::ty::{EarlyBinder, InternalSubsts, SubstsRef};
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::Namespace;
 use rustc_hir::def_id::{CrateNum, DefId};

compiler/rustc_middle/src/ty/layout.rs

@@ -1,7 +1,6 @@
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::mir::{GeneratorLayout, GeneratorSavedLocal};
 use crate::ty::normalize_erasing_regions::NormalizationError;
-use crate::ty::subst::Subst;
 use crate::ty::{
     self, layout_sanity_check::sanity_check_layout, subst::SubstsRef, EarlyBinder, ReprOptions, Ty,
     TyCtxt, TypeVisitable,

compiler/rustc_middle/src/ty/mod.rs

@@ -89,9 +89,9 @@ pub use self::sty::BoundRegionKind::*;
 pub use self::sty::{
     Article, Binder, BoundRegion, BoundRegionKind, BoundTy, BoundTyKind, BoundVar,
     BoundVariableKind, CanonicalPolyFnSig, ClosureSubsts, ClosureSubstsParts, ConstVid,
-    EarlyBinder, EarlyBoundRegion, ExistentialPredicate, ExistentialProjection,
-    ExistentialTraitRef, FnSig, FreeRegion, GenSig, GeneratorSubsts, GeneratorSubstsParts,
-    InlineConstSubsts, InlineConstSubstsParts, ParamConst, ParamTy, PolyExistentialProjection,
+    EarlyBoundRegion, ExistentialPredicate, ExistentialProjection, ExistentialTraitRef, FnSig,
+    FreeRegion, GenSig, GeneratorSubsts, GeneratorSubstsParts, InlineConstSubsts,
+    InlineConstSubstsParts, ParamConst, ParamTy, PolyExistentialProjection,
     PolyExistentialTraitRef, PolyFnSig, PolyGenSig, PolyTraitRef, ProjectionTy, Region, RegionKind,
     RegionVid, TraitRef, TyKind, TypeAndMut, UpvarSubsts, VarianceDiagInfo,
 };

compiler/rustc_middle/src/ty/normalize_erasing_regions.rs

@@ -10,8 +10,7 @@
 use crate::mir;
 use crate::traits::query::NoSolution;
 use crate::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeFolder};
-use crate::ty::subst::{Subst, SubstsRef};
-use crate::ty::{self, EarlyBinder, Ty, TyCtxt};
+use crate::ty::{self, EarlyBinder, SubstsRef, Ty, TyCtxt};
 
 #[derive(Debug, Copy, Clone, HashStable, TyEncodable, TyDecodable)]
 pub enum NormalizationError<'tcx> {

compiler/rustc_middle/src/ty/print/mod.rs

@@ -1,4 +1,4 @@
-use crate::ty::subst::{GenericArg, Subst};
+use crate::ty::GenericArg;
 use crate::ty::{self, DefIdTree, Ty, TyCtxt};
 
 use rustc_data_structures::fx::FxHashSet;

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -1,9 +1,9 @@
 use crate::mir::interpret::{AllocRange, GlobalAlloc, Pointer, Provenance, Scalar};
-use crate::ty::subst::{GenericArg, GenericArgKind, Subst};
 use crate::ty::{
     self, ConstInt, DefIdTree, ParamConst, ScalarInt, Term, TermKind, Ty, TyCtxt, TypeFoldable,
     TypeSuperFoldable, TypeSuperVisitable, TypeVisitable,
 };
+use crate::ty::{GenericArg, GenericArgKind};
 use rustc_apfloat::ieee::{Double, Single};
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_data_structures::sso::SsoHashSet;

compiler/rustc_middle/src/ty/relate.rs

@@ -5,8 +5,8 @@
 //! subtyping, type equality, etc.
 
 use crate::ty::error::{ExpectedFound, TypeError};
-use crate::ty::subst::{GenericArg, GenericArgKind, Subst, SubstsRef};
 use crate::ty::{self, ImplSubject, Term, TermKind, Ty, TyCtxt, TypeFoldable};
+use crate::ty::{GenericArg, GenericArgKind, SubstsRef};
 use rustc_hir as ast;
 use rustc_hir::def_id::DefId;
 use rustc_span::DUMMY_SP;

compiler/rustc_middle/src/ty/sty.rs

@@ -3,7 +3,7 @@
 #![allow(rustc::usage_of_ty_tykind)]
 
 use crate::infer::canonical::Canonical;
-use crate::ty::subst::{GenericArg, InternalSubsts, Subst, SubstsRef};
+use crate::ty::subst::{GenericArg, InternalSubsts, SubstsRef};
 use crate::ty::visit::ValidateBoundVars;
 use crate::ty::InferTy::*;
 use crate::ty::{
@@ -551,7 +551,7 @@ impl<'tcx> GeneratorSubsts<'tcx> {
         layout.variant_fields.iter().map(move |variant| {
             variant
                 .iter()
-                .map(move |field| EarlyBinder(layout.field_tys[*field]).subst(tcx, self.substs))
+                .map(move |field| ty::EarlyBinder(layout.field_tys[*field]).subst(tcx, self.substs))
         })
     }
 
@@ -915,77 +915,6 @@ impl<'tcx> PolyExistentialTraitRef<'tcx> {
     }
 }
 
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
-#[derive(Encodable, Decodable, HashStable)]
-pub struct EarlyBinder<T>(pub T);
-
-/// For early binders, you should first call `subst` before using any visitors.
-impl<'tcx, T> !TypeFoldable<'tcx> for ty::EarlyBinder<T> {}
-impl<'tcx, T> !TypeVisitable<'tcx> for ty::EarlyBinder<T> {}
-
-impl<T> EarlyBinder<T> {
-    pub fn as_ref(&self) -> EarlyBinder<&T> {
-        EarlyBinder(&self.0)
-    }
-
-    pub fn map_bound_ref<F, U>(&self, f: F) -> EarlyBinder<U>
-    where
-        F: FnOnce(&T) -> U,
-    {
-        self.as_ref().map_bound(f)
-    }
-
-    pub fn map_bound<F, U>(self, f: F) -> EarlyBinder<U>
-    where
-        F: FnOnce(T) -> U,
-    {
-        let value = f(self.0);
-        EarlyBinder(value)
-    }
-
-    pub fn try_map_bound<F, U, E>(self, f: F) -> Result<EarlyBinder<U>, E>
-    where
-        F: FnOnce(T) -> Result<U, E>,
-    {
-        let value = f(self.0)?;
-        Ok(EarlyBinder(value))
-    }
-
-    pub fn rebind<U>(&self, value: U) -> EarlyBinder<U> {
-        EarlyBinder(value)
-    }
-}
-
-impl<T> EarlyBinder<Option<T>> {
-    pub fn transpose(self) -> Option<EarlyBinder<T>> {
-        self.0.map(|v| EarlyBinder(v))
-    }
-}
-
-impl<T, U> EarlyBinder<(T, U)> {
-    pub fn transpose_tuple2(self) -> (EarlyBinder<T>, EarlyBinder<U>) {
-        (EarlyBinder(self.0.0), EarlyBinder(self.0.1))
-    }
-}
-
-pub struct EarlyBinderIter<T> {
-    t: T,
-}
-
-impl<T: IntoIterator> EarlyBinder<T> {
-    pub fn transpose_iter(self) -> EarlyBinderIter<T::IntoIter> {
-        EarlyBinderIter { t: self.0.into_iter() }
-    }
-}
-
-impl<T: Iterator> Iterator for EarlyBinderIter<T> {
-    type Item = EarlyBinder<T::Item>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        self.t.next().map(|i| EarlyBinder(i))
-    }
-}
-
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, TyEncodable, TyDecodable)]
 #[derive(HashStable)]
 pub enum BoundVariableKind {

compiler/rustc_middle/src/ty/subst.rs

@@ -497,18 +497,79 @@ impl<'tcx, T: TypeVisitable<'tcx>> TypeVisitable<'tcx> for &'tcx ty::List<T> {
     }
 }
 
-// Just call `foo.subst(tcx, substs)` to perform a substitution across `foo`.
-#[rustc_on_unimplemented(message = "Calling `subst` must now be done through an `EarlyBinder`")]
-pub trait Subst<'tcx>: Sized {
-    type Inner;
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+#[derive(Encodable, Decodable, HashStable)]
+pub struct EarlyBinder<T>(pub T);
 
-    fn subst(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> Self::Inner;
+/// For early binders, you should first call `subst` before using any visitors.
+impl<'tcx, T> !TypeFoldable<'tcx> for ty::EarlyBinder<T> {}
+impl<'tcx, T> !TypeVisitable<'tcx> for ty::EarlyBinder<T> {}
+
+impl<T> EarlyBinder<T> {
+    pub fn as_ref(&self) -> EarlyBinder<&T> {
+        EarlyBinder(&self.0)
+    }
+
+    pub fn map_bound_ref<F, U>(&self, f: F) -> EarlyBinder<U>
+    where
+        F: FnOnce(&T) -> U,
+    {
+        self.as_ref().map_bound(f)
+    }
+
+    pub fn map_bound<F, U>(self, f: F) -> EarlyBinder<U>
+    where
+        F: FnOnce(T) -> U,
+    {
+        let value = f(self.0);
+        EarlyBinder(value)
+    }
+
+    pub fn try_map_bound<F, U, E>(self, f: F) -> Result<EarlyBinder<U>, E>
+    where
+        F: FnOnce(T) -> Result<U, E>,
+    {
+        let value = f(self.0)?;
+        Ok(EarlyBinder(value))
+    }
+
+    pub fn rebind<U>(&self, value: U) -> EarlyBinder<U> {
+        EarlyBinder(value)
+    }
+}
+
+impl<T> EarlyBinder<Option<T>> {
+    pub fn transpose(self) -> Option<EarlyBinder<T>> {
+        self.0.map(|v| EarlyBinder(v))
+    }
 }
 
-impl<'tcx, T: TypeFoldable<'tcx>> Subst<'tcx> for ty::EarlyBinder<T> {
-    type Inner = T;
+impl<T, U> EarlyBinder<(T, U)> {
+    pub fn transpose_tuple2(self) -> (EarlyBinder<T>, EarlyBinder<U>) {
+        (EarlyBinder(self.0.0), EarlyBinder(self.0.1))
+    }
+}
+
+pub struct EarlyBinderIter<T> {
+    t: T,
+}
+
+impl<T: IntoIterator> EarlyBinder<T> {
+    pub fn transpose_iter(self) -> EarlyBinderIter<T::IntoIter> {
+        EarlyBinderIter { t: self.0.into_iter() }
+    }
+}
+
+impl<T: Iterator> Iterator for EarlyBinderIter<T> {
+    type Item = EarlyBinder<T::Item>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.t.next().map(|i| EarlyBinder(i))
+    }
+}
 
-    fn subst(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> Self::Inner {
+impl<'tcx, T: TypeFoldable<'tcx>> ty::EarlyBinder<T> {
+    pub fn subst(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> T {
         let mut folder = SubstFolder { tcx, substs, binders_passed: 0 };
         self.0.fold_with(&mut folder)
     }